The present invention relates to means for reducing the amount of damaging hydrogen halide gases present in the stack exhausts of incinerators for trash and industrial waste.
In order to satisfy the requirements of environmental protection laws relating to the damaging hydrogen halide content of exhaust gases generated by the burning of solid, liquid, and gas waste from home and industry, it is known to provide in the path of the exhaust gas, in addition to the mechanical or electrical filter for separating out the fly ash, a special exhaust wet scrubbing apparatus for reducing the content of the damaging gas. While a large portion of the hydrogen halide, which is readily soluble in water, present in the exhaust gases is removed by such wet scrubbing, nevertheless this leads to an undesirably high concentration of halides in the effluent from the system. Removal from the effluent would require neutralization and a rather costly heating of the fluid to form removable agglomerates of the precipitate which would be formed by neutralization. The wet scrubbing cannot simultaneously remove the particulates and the damaging gases, and it is always used together with a filter, such as an electrostatic precipitator. This filter brings with it the further complicating problem of environmentally acceptable disposal. Additionally, since even on being warmed, the exhaust gases leave the stack saturated with water vapor, this leads to what some refer to as stack gas "rain" on cold weather days.
In order to deal with the above-mentioned problems, it is known to use a dry scrubbing process. In this process a dry scrubbing agent, such as a magnesium-based caustic lime, is blown into the exhaust gas stream of a waste incinerator combustion chamber to bind to damaging gases, such as primarily hydrogen chloride (HCl), but also hydrogen fluoride (HF), sulfur dioxide (SO.sub.2), and sulfur trioxide (SO.sub.3). The blowing of the powdered agent into the combustion chamber is accomplished through a plurality of injection lances extending from a secondary air supply into the combustion chamber in the lower portion of the back wall.
The known approach of injecting the dry scrubbing agent into the combustion chamber of the incinerator, however, has the disadvantage that for thermodynamic reasons the hydrogen halide gases don't bind well to the scrubbing agent at the high temperatures present in the chamber. That is, the interaction of the agent with the damaging gas components of the exhaust gases takes place relatively slowly and with little intensity.
In other presently known arrangements of the described type in which hydrogen chloride is likewise removed by means of a dry scrubbing agent, the powdered agent is introduced into a specially provided reactor vessel installed between the combustion chamber and an electrostatic precipitator, and only there caused to interact with the exhaust gases.
With such an arrangement, the interaction of the agent with the exhaust gases is no longer significantly influenced by the combustion temperature. However, there is still present the disadvantage that the relatively large special reactor vessel required is costly, requires considerable space, and adds to the maintenance of the entire incinerator installation.